Fix potential memory leak in test_hs_auth_cookies().

This patch fixes a potential memory leak in test_hs_auth_cookies() if a
test-case fails and we goto the done label where no memory clean up is
done.

See: Coverity CID 1437453

src/test/test_hs.c

@@ -446,10 +446,10 @@ test_hs_auth_cookies(void *arg)
 #define TEST_COOKIE_ENCODED_STEALTH "YWJjZGVmZ2hpamtsbW5vcB"
 #define TEST_COOKIE_ENCODED_INVALID "YWJjZGVmZ2hpamtsbW5vcD"
 
-  char *encoded_cookie;
+  char *encoded_cookie = NULL;
   uint8_t raw_cookie[REND_DESC_COOKIE_LEN];
   rend_auth_type_t auth_type;
-  char *err_msg;
+  char *err_msg = NULL;
   int re;
 
   (void)arg;
@@ -495,6 +495,9 @@ test_hs_auth_cookies(void *arg)
   tor_free(err_msg);
 
  done:
+  tor_free(encoded_cookie);
+  tor_free(err_msg);
+
   return;
 }